The configuration of modern sound amplification equipment that creates surround sound involves functional separation of channels. Such an audio system includes front and rear speakers, a center channel and a subwoofer.
The latter serves to create additional sound effects in the lower frequency range from 20 to 180 Hz. Basically, this additional device is used when watching video programs and films that contain scenes of explosions, launches of space rockets and similar situations, when sounding them you need to shake the air quite intensively.
As a rule, subwoofers are designed according to the active principle, that is, they have their own built-in amplifier, power supply and adjustment. The controls and settings include two main knobs: “Level” (Level) and “Cutoff Frequency” (Crossover Frequency). The purpose of the level knob is quite clear, it is the regulation of the intensity of the sound signal. But why a second setting is needed, not everyone understands.
Unlike broadband
loudspeakers, the subwoofer has a
frequency range limited to the upper edge
. In turn, the bass is conditionally divided into deep - up to 40 Hz, medium - up to 80 Hz, and high - up to 160 Hz. The depth of the achieved acoustic effect depends on which cutoff frequency is set. In some cases, participating in the high bass spectrum creates a softer sound, for example, when listening to music or watching movies that are not loaded with special effects. If a more severe impact on the nervous system of the viewer is required, for example, when collapsing buildings or exploding planets appear, then the cutoff frequency of the subwoofer can be shifted closer to the infrared range.
Technically, implementing the upper frequency limit is a simple task. From the course of physics it is known that capacitances have a filtering property with respect to low frequencies, and inductances have high properties. Thus, the simplest LC filter can quite efficiently select the desired part of the range, while reducing the signal level of the unwanted spectrum. In order to “keep out” the high and medium frequencies at the input of the subwoofer, it is enough to include a small capacitor in parallel to the input terminals - a few picofarads. But such a primitive filter will give too smooth a decrease in the amplitude-frequency characteristic, so in practice their design is somewhat more complicated.
In addition, the cutoff frequency is provided by filtering the output signal going to a powerful loudspeaker. To do this, inside the case next to the speaker is another board with capacitors and inductances.
The cutoff frequency of the low-pass filters (low-pass filters) should ideally be regulated, although in low-cost systems such a function may not be.
Correctly adjusting the subwoofer in relation to the other acoustic components of the home theater system is a matter of patience and thoroughness. Such a regulation is considered good when the bass emitted by the front and rear speakers is complemented by the infra-low frequencies broadcast by it, rather than “arguing” among themselves who is stronger. The principle “the louder the better” does not work here.
Thus, the cutoff frequency is an important setting to ensure the correct and consistent sound of the entire system.